Two days and no answer...
If you still have a question, I strongly suggest showing examples (use the Code tags) and explaining better.

I had to read 4 times your sentence (specially the part with "hexa decimal value" and "an alphanumeric value"),
When I realized maybe you received a "USAGE COMP" value (to use COBOL language) and want it converted to "USAGE DISPLAY".
But then, what about the encoding ?

You were asked to use the code tags when presenting you/data/code. You were even given a link to how to use them. Please use them in future for anything that you might see on 3279 screen. I have coded your code for you - this time.

This option converts the application data in the message to conform to the CodedCharSetId and Encoding values specified in the MsgDesc parameter on the MQGET call. The data is converted before it is copied to the Buffer parameter.